This invention relates to a stator blade pivoting arrangement in a turbomachine.
The stator blades, stationary in a turbomachine and used to rectify the gas flow before the next rotor blade stage, may be of the variable locking type, i.e. their orientation is controlled as a function of the operating mode of the machine. They are then mounted on outer pivots which project outside the stator casing and are connected to connecting rods rotated at will by a common control ring, surrounding the stator casing. The rotation of the connecting rods produces a similar rotation of the blades. The transmission of the rotation is acquired by a suitable adjustment liable to comprise mutual support of plane faces established on an end section of the pivot of the blade and on a bore at the end of the connecting rod: this end section and the bore are frequently squares.
The documents U.S. Pat. Nos. 4,767,264 and 4,668,165-A disclose connecting rod arrangements sufficiently thin to be flexible to the twisting to which they are subjected by the rotation of the control ring. These connecting rods are equipped with lateral ribs curved like tongs and which penetrate into the grooves of the pivots. These ribs are responsible for rotating the pivots with an engagement which is only slightly different to that of the square sections.
However, it is observed that the slightest adjustment play between the bore of the connecting rod and the pivot of the blade delays the rotational drive markedly, and a drive defect of several tenths of an angular degree is frequently reached. Since the blade should be oriented with great precision in order to obtain a good machine output, it can be concluded that an improvement is desirable to reduce the square adjustment play.
A solution is offered with the invention, which consists in its broadest definition of a stator blade pivoting arrangement in a turbomachine, comprising a blade pivot having one end projecting outside the stator and comprising a plane face section, and a control connecting rod engaged onto the end of the blade pivot via a bore limited by plane faces associated with the plane faces of the pivot, characterised in that it comprises a spring stressed between the pivot and the connecting rod and arranged so as to press one of the plane faces of the pivot against one of the plane faces of the connecting rod.
The above-mentioned documents do not clearly disclose the nature of the ribs, and in particular their rigidity. It is not stated that they have an elasticity which would be used to keep them in contact with the base of the grooves and ensure the angular position of the blade pivot with respect to the connecting rod with sufficient force.
The assemblies in these documents are also of a special type. The spring according to the invention is an autonomous part, distinct from the rest of the conventional square section assembly which does not need to be modified, the spring being simply added.
It is favourably envisaged that the springs will comprise a bored washer placed on the connecting rod and engaged around the end of the blade pivot, and a flexible edge of the washer, engaged on an edge face of the connecting rod opposite one of the faces of the pivot against which the washer abuts, making with the washer a wider angle than in the idle state of the spring.